[PATCH 3.18 20/31] net/rose: fix NULL ax25_cb kernel panic

From: Greg Kroah-Hartman
Date: Mon Feb 04 2019 - 05:38:34 EST

3.18-stable review patch. If anyone has any objections, please let me know.


From: Bernard Pidoux <f6bvp@xxxxxxx>

[ Upstream commit b0cf029234f9b18e10703ba5147f0389c382bccc ]

When an internally generated frame is handled by rose_xmit(),
rose_route_frame() is called:

if (!rose_route_frame(skb, NULL)) {
return NETDEV_TX_OK;

We have the same code sequence in Net/Rom where an internally generated
frame is handled by nr_xmit() calling nr_route_frame(skb, NULL).
However, in this function NULL argument is tested while it is not in
Then kernel panic occurs later on when calling ax25cmp() with a NULL
ax25_cb argument as reported many times and recently with syzbot.

We need to test if ax25 is NULL before using it.

Built kernel with CONFIG_ROSE=y.

Signed-off-by: Bernard Pidoux <f6bvp@xxxxxxx>
Acked-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Reported-by: syzbot+1a2c456a1ea08fa5b5f7@xxxxxxxxxxxxxxxxxxxxxxxxx
Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
Cc: Ralf Baechle <ralf@xxxxxxxxxxxxxx>
Cc: Bernard Pidoux <f6bvp@xxxxxxx>
Cc: linux-hams@xxxxxxxxxxxxxxx
Cc: netdev@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
net/rose/rose_route.c | 5 +++++
1 file changed, 5 insertions(+)

--- a/net/rose/rose_route.c
+++ b/net/rose/rose_route.c
@@ -849,6 +849,7 @@ void rose_link_device_down(struct net_de

* Route a frame to an appropriate AX.25 connection.
+ * A NULL ax25_cb indicates an internally generated frame.
int rose_route_frame(struct sk_buff *skb, ax25_cb *ax25)
@@ -866,6 +867,10 @@ int rose_route_frame(struct sk_buff *skb

if (skb->len < ROSE_MIN_LEN)
return res;
+ if (!ax25)
+ return rose_loopback_queue(skb, NULL);
frametype = skb->data[2];
lci = ((skb->data[0] << 8) & 0xF00) + ((skb->data[1] << 0) & 0x0FF);
if (frametype == ROSE_CALL_REQUEST &&